This invention relates to rotating pumps or compressors of the scroll type and is more particularly directed to an improved construction involving an improved scroll tip seal.
Scroll type compressors have been known, in principle, for several decades. In general, a scroll-type compressor or similar machine comprises a pair of mating scrolls, each of which has an involute spiral wrap of similar shape, mounted on respective base plates. Normally, one scroll is held fixed, and the other is movable, to orbit but not rotate, about the axis of the fixed scroll, being held by an Oldham ring or other anti-rotating structure. The walls of the two involute wraps define crescent-shaped volumes which become smaller and smaller and move from the outside to the center of the mating scrolls as the orbiting scroll revolves. A compressible fluid, such as a refrigerant gas, can be introduced at the periphery of the spiral wraps, and is compressed as it is moved under the orbiting motion of the device. The compressed fluid is then discharged at the center. By introducing a compressed fluid at the center and permitting its expansion to drive the device, the scroll machine can be used as a motor.
The orbiting motion of the moving scroll means that at the tip of the scroll wrap of both the orbiting and the stationary scroll there is a convoluted interface across which the fluid being compressed can leak from the high pressure side to the low pressure side of these devices. To minimize leakage at the scroll tip the devices have been manufactured with extremely tight tolerances but it still has been found desirable to provide a tip seal to further reduce leakage. The standard type O-ring materials placed in a slot in the scroll wrap tips have been unsatisfactory for a number of reasons, principally swelling of the material and consequent loss of spring rate such that the sealing effectiveness of the material is lost or the material disintegrates and inhibits the orbiting action of the movable scroll.
A proposed solution to the tip seal problem in the past has been an elongated "C" shaped cross section spring placed in a groove in the tip of the scroll from one end to the other. The spring is made from a sheet of spring steel formed into a "C" shaped cross section and coiled to match the scroll. This solid continuous spring member has been usually covered with a sealing and anti-friction Teflon based material, to enhance the sealing action of the spring against the base of the opposite scroll and to minimize frictional losses under the heat generated by the fluid compressing action. It has been found that the "C" shaped cross section spring has provided good seal compliance and has not been subject to loss of spring rate. It has, however, offered a leakage path through the center of the "C" from the high side center of the scroll to the low side periphery of the scroll by leakage across the tip into the center of the spring. This has reduced the effectiveness of the "C" shaped elongated spring tip seal.